Prior inventions relating to an automatic transmission using a gear-type shifting means include one in which the top-speed gear of the gear-type automatic transmission is engaged/disengaged using a multi-disc clutch and when a shift is performed, the engine speed of the corresponding vehicle is controlled by slipping the multi-disc clutch and is thus synchronized with the rotational speed of the output shaft so as to accomplish the shift smoothly. Such prior art is disclosed in, for example, Japanese Laid-Open Patent Application Publication No. Sho 61-45163.
The gear-type automatic transmission described above, however, poses the problems that if the torque capacity of the multi-disc clutch is small, when a shift is made at a high output shaft torque, the difference between this torque and the torque that the multi-disc clutch can generate will be transmitted to the output shaft as a change in torque, thus making the passengers (including the driver) feel uncomfortable, and that in case of trouble with the driving source of the actuators which drive the automatic transmission, if the engine torque is not transmitted to the output shaft properly, this can cause the engine to stall or the engine speed to increase abruptly, thus resulting in the vehicle not operating properly.